Does having an SSL certificate mean I won’t get hacked? If not, then what does the SSL certificate do?

Having an SSL certificate installed on your server is not a guarantee that it won’t be hacked. The SSL certificate and HTTPS protocol will ensure that traffic between your site and your web users are encrypted to minimise the risk of eavesdropping when the traffic is intercepted. It does not secure your web server on the server’s operating system (OS) and application level — you still need to harden your OS, regularly patch your OS and application to ensure the security of your site on the server and application level.